Question

I using the following :convert_options

-auto-orient -gravity center -background transparent -extent '50x50>'

for what of my has_attached_file calls, what I WANT to do is rather than using transparent, I’d like to set the background color of the image to the color that lives at 0,0 of the image.

Using

convert rose: -format "%[pixel:u.p{0,0}]" info:-

I get the output

srgb(48,47,45)

which is great, but I’m unable to use that in place of transparent in the actual call..

Can anyone help with how I can pull this off?

Answer 1

Wrote a custom interpolator for this.

module Paperclip
  class BgExtrapolator < Processor
    def initialize(file, options = {}, attachment = nil)
      super

      @file             = file
      @instance         = options[:instance]
      @current_format   = File.extname(@file.path)
      @basename         = File.basename(@file.path, @current_format)
    end

    def make
      src = @file
      dst = Tempfile.new([@basename, @format ? ".#{@format}" : ''])
      dst.binmode

      begin
        # grab the image
        logo = Magick::Image.read(src.path).first

        # determine the color of the upper left most pixel
        bg_color = logo.pixel_color(0,0)

        # construct an rgba value to provide to imagemagick
        bg_color_value = "rgba(#{bg_color.red >> 8},#{bg_color.green >> 8},#{bg_color.blue >> 8},#{bg_color.to_hsla[3]})"

        parameters = []
        parameters << ":source"
        parameters << "-resize '#{options[:geometry].to_s}' -auto-orient -gravity center -background '#{bg_color_value}' -extent '#{options[:geometry].to_s}'"
        parameters << ":dest"

        # clean the command
        parameters = parameters.flatten.compact.join(" ").strip.squeeze(" ")

        # run the command
        success = convert(parameters, :source => File.expand_path(src.path), :dest => File.expand_path(dst.path))
      rescue Cocaine::ExitStatusError => e
        raise Paperclip::Error, "There was an error processing the thumbnail for #{@basename}" if @whiny
      rescue Cocaine::CommandNotFoundError => e
        raise Paperclip::Errors::CommandNotFoundError.new("Could not run the `convert` command. Please install ImageMagick.")
      end

      dst
    end
  end
end